The present invention relates to an improved apparatus and method for the photolytic oxidation of organic residues in water, and more particularly to the oxidation of those residues by adding an oxidizing agent to the water to be treated, then exposing the water to ultraviolet light.
Systems for treating water by adding an oxidizing agent, such as hydrogen peroxide (H.sub.2 O.sub.2) or ozone (O.sub.3), and then oxidizing organic impurities in the water by exposing the water to ultraviolet light are well known. The ultraviolet light serves to catalyze the oxidation of the organic compounds, converting them to water and carbon dioxide.
Photolytic oxidation of wastewater streams is conventionally carried out in a tank-like reactor containing an ultraviolet light source. A measured amount of an oxidizing agent is added to the incoming stream. As the water proceeds through the reactor, the desired oxidation reaction takes place.
In many situations, interruption of the flow of water through the reactor is to be avoided, if possible, because such interruption can inconvenience or disrupt other operations that generate or supply the water. This is particularly true in applications where treatment of the water in the reactor is simply one stage in a multi-stage process which generates the wastewater. At the same time, it is probably impossible to build a reactor with today's technology that is totally maintenance free; accordingly, conventional reactors require periodic shutdown for maintenance. One of the major maintenance requirements of this type of reactor is replacement of the ultraviolet lamps.
Reactors of the type to which the present invention relates typically utilize low-pressure metal vapor lights. These ultraviolet lights have a limited lifetime, and at some point, simply burn out. The same is true of other conventional ultraviolet light sources, such as incandescent lamps, medium pressure and high pressure metal vapor lamps, and arc lamps. Burned out lamps, of course, require replacement. Safe practice dictates that the power to the lamps be disabled prior to replacement. One reason for this is, of course, the desire to avoid the possibility of electrical shock from handling wires and connectors that are electrically energized. Another reason that is of particular concern when using ultraviolet lamps is the avoidance of the potentially harmful exposure of maintenance workers and others to ultraviolet radiation. Such radiation can result in ocular damage and epidermal burning.
For this reason, the lamps in the reactor are typically extinguished while lamp or other maintenance is in process. Unfortunately, while the lamps are out, no significant oxidation of the organic impurities in the water occurs. In many instances, the water is being treated in order to satisfy governmental regulations, and disposal of water that has not been adequately treated constitutes a violation of those regulations. Thus, while lamp maintenance is in progress, the water flow through the reactor must be interrupted, often with serious disruption of other processes that generate the water in question.
Another concern in systems of this type is accidental exposure of workers to the ultraviolet light. As set forth above, such exposure can damage the health of the worker and should be avoided. Although protective clothing and eyewear can minimize the consequences of exposure to strong ultraviolet light, it is unreasonable to expect that all workers and others in the proximity of the reactor would have such protective gear. Moreover, protective gear is generally uncomfortable or inconvenient and, thus, is not always worn in situations that should require the use of such gear.
Accordingly, one object of the present invention is to provide a method and apparatus for photolytic oxidation of organic residues in water that can operate continuously without requiring shutdown for most routine maintenance.
Another object of the present invention is the provision of a reactor that includes safety features designed to prevent unauthorized access to reaction chambers in which there is a danger of exposure to ultraviolet light and to prevent accidental exposure of maintenance personnel and other workers to potentially harmful ultraviolet radiation.
Other objects, features, and advantages of the present invention will become apparent in light of the following explanation.